Multi-carrier transmission schemes such as Orthogonal Frequency Division Multiplexing (OFDM) are being deployed in, or proposed for, a wide range of communications systems such as wireless networking, radio and television broadcasting and multicasting, and Fourth Generation (4G) communications networks. In a multi-carrier transmission scheme a number of orthogonal carrier signals are used. Data to be transmitted is divided into parallel data streams, one stream for each carrier, and data symbols are formed. Each carrier is modulated using a modulation scheme such as Quadrature Amplitude Modulation (QAM) or Quadrature Phase Shift Keying (QPSK). Multi-carrier transmission schemes are popular because they are particularly robust where the channel between a transmitter and a receiver suffers from impairments such as time dispersion and/or frequency selective fading.
One problem facing multi-carrier transmission schemes is their susceptibility to frequency offsets, phase noise, and Doppler effects when the channel is rapidly changing. These problems can cause inter-carrier interference (ICI) between the multiple carriers, and can result in bit errors.
Various techniques are known to cancel inter-carrier interference but they generally require significant processing resources with complexity that is of the order of O(N.log2(N)) to O(N3), where N is the symbol length. This makes the known techniques unsuitable for use in terminals which have limited processing resources or power budgets. WO 2006/111843 describes an inter-carrier interference reduction technique which uses windowing of the received signal and then uses a matrix computation to estimate the ICI impact on each carrier by means of sequential channel estimations, after time-domain to frequency-domain processing.